1. Field of the Invention
The present invention relates to a composite semiconductor device in which arrays such as LED arrays are combined with driver circuits, an LED print head that employs the composite semiconductor device, and an image forming apparatus that employs the LED head.
2. Description of the Related Art
Among conventional electrophotographic printers is one that incorporates an LED type exposing unit. An LED type exposing unit incorporates a plurality of LED array chips, each of which includes a plurality of light emitting diodes (LEDs).
Many printers of late are capable of printing not only characters but also images. Printing images with high resolution places great demands on printers, leading to increasing number of LEDs used in an exposing unit. This increases the array density of LEDs array chips and driver circuits incorporated in the exposing unit.
Japanese patent Laid-Open No 2004-179641 discloses one way of meeting these demands without mounting individual LED arrays and driver circuits on a printed circuit board. Driver circuits are formed on a semiconductor substrate, and LED array chips are bonded on the semiconductor substrate, thereby preparing a composite semiconductor device. The composite semiconductor devices are then mounted on a printed circuit board. Then, the composite semiconductors are electrically connected by bonding wires to the circuit board.
The composite semiconductor device of the aforementioned configuration suffers from the problem in that light emitting regions emit light not only in a direction in which the light should be emitted but also in other directions in which light should not be emitted. The light emitted in unwanted directions may be reflected by, for example, bonding wires, disturbing an electrostatic latent image formed by the LED print head.